1. Field of the Invention
The present invention relates in general to an image display apparatus, more particularly, to a digital TV and a channel setting method thereof, wherein digital channel scan is not performed on channel numbers reserved for analog broadcast.
2. Discussion of the Background Art
In general, when an analog broadcast is seen on a big screen TV, image quality is lowered, and the number of allocated channels is limited to 80 including VHF (very high frequency and UHF (ultra high frequency) channel band, so an analog TV has its limit as a single direction medium.
To overcome the problems of the analog broadcast system, a digital broadcast system has been developed. The digital broadcast remarkably improved the image quality of the analog broadcast, offering an image more than twice as clear as the analog broadcast. And, since there is no interference between adjacent channels, the digital television provides full surfing capability, using every channel not used.
Another merit of the digital broadcast is that it can freely transfer, process, provide, and store contents (video, audio, data) without data loss. Thus, a lot of services the analog broadcast system could not provide are now available.
For example, the digital broadcast does not have a ghost that usually occurs as an analog TV signal goes through the air or significant image deterioration in image quality (e.g., bleeding), so that it can provide services with high image quality and high sound quality.
The high image quality refers to clear, crisp images equivalent to 35 mm film images. Generally, a HDTV (High Definition Television) provides such images. On the other hand, a SDTV (Standard Density Television) provides nearly 16 mm film images, yet they are still better than the images in the analog broadcast.
The image gets clearer as the number of pixels, the smallest resolvable rectangular area of an image on a screen, is higher. Normally, the HDTV has resolution of 2 million pixels (resolution: 1920×1080), and the SDTV has resolution of 350,000 pixels (resolution: 720×480). The high sound quality refers to the CD-quality stereo sound quality or 3D surround sound quality of film Considering that 6 speakers are used to produce the 3D surround sound, the digital TV brings viewers stereo, real-time effects that could find in a movie theater only.
Because of these advantages, the digital broadcast system has grown more and more popular. Although the analog broadcast and the digital broadcast will go on the air together by 2010, the digital broadcast will ultimately replace the analog broadcast at the end.
Right now, digital TVs provide automatic channel setup environments to enable viewers to tune into both analog and digital broadcasts at the same time.
That is, after checking the statue of an antenna currently being used to receive TV signals, the digital TV sets the channels in order of over-the-air broadcast/cable broadcast/digital TV air broadcast/digital TV cable broadcast.
FIG. 1 diagrammatically illustrates frequencies of channels currently being used for broadcasting.
As shown in FIG. 1, channels 2-69 are allocated to the over-the-air broadcast TV programs, and channels 1, 14-125 are allocated to the cable broadcasts. Therefore, the digital TV checks a synchronous signal with a channel in a frequency range corresponding to each number. Thus, if a synchronous signal exists in a certain channel, the digital TV remembers the channel, but if not, it does not remember the channel.
Here, the over-the-air broadcasts and the digital TV air broadcasts use the same frequency band, and the cable broadcasts and the digital TV cable broadcasts use the same frequency band.
Therefore, digital broadcasts cannot be sent to the frequency band already being used for analog broadcasts. This means that it is useless to scan digital broadcasts on analog broadcast signals.
Nevertheless, when the automatic channel scanning is set, the related art digital TV scans digital broadcasts even in the frequency band for analog broadcasts. Thus, it takes more time than necessary to set channels.